• Duplication of the appendix is a rare anomaly that has been reported fewer than 60 times. Three anatomic types of appendiceal duplications have been described—each the result of a different embryologic occurrence. A unique case of appendiceal duplication is presented, in which the duplication caused a constricting lesion of the colon and mimicked carcinoma. The anomalous appendix in this patient was not compatible with any of the previously described types of appendiceal duplications.